Xerothermographic process

ABSTRACT

A reproduction method wherein a heat-sensitive layer, upon receiving a uniform electrostatic charge, is exposed to a thermal image of the document being copied, such exposure serving to selectively dissipate the uniform charge on the heat-sensitive layer to produce a latent electrostatic image thereon. The latent image is rendered visible by conventional xerographic development techniques.

United States Patent 11 1 3,673,961 Jarvis 1 1 July 4, 1972 [541 XEROTHERMOGRAPHIC PROCESS 2,995,085 8/1961 Walkup ..101/1492 2,927,210 3/1960 OMara ..250/65 [72] James Jams 3,012,141 12/1961 Thomsizer.... ..250/65 [73] Assignee: Eastman Kodak Company, Rochester, 2,576,047 1 1951 Schaffefl /6 NY. 2,647,464 8/1953 Ebert .250/65 1 2,817,765 12/1957 Hayford et al 250/65 1 [221 led: 1960 2,934,649 4/1960 Walkup ...250/65 1 21 APPL 25 10 2,939,787 6/1960 Giaimo ..250/65 1 Primary Examiner-Edgar S. Burr [52] 11.8. C1 ..101/465, 250/65 T, 101/470, R F k s i h d F, M, Emerson Holmes 101/463, 338/25 [51] Int. Cl ..B4lm 5/18 [57] ABSTRACT [58] Field ofSearch ..250/65.1; 101/D1G. l3; 338/7,

338/9, 28 25 A reproductxon method wherem a heat-sensitive layer, upon receiving a uniform electrostatic charge, is exposed to a ther- [56] Reierences Cited mal image of the document being copied, such exposure serving to selectively dissipate the uniform charge on the heat-sen- UNITED TAT S N S sitive layer to produce a latent electrostatic image thereon.

2,993,787 7/1961 3,205,354 9/1965 Glas eta]. 2,719,481

Sugarman ..10l/l49.2 UX ..lOl/DIG.13 Botthof et al. ..10l/l49.2

The latent image is rendered visible by conventional xerographic development techniques.

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fM/JA W/(W' m ATTORNEYS XEROTHERMOGRAPIIIC PROCESS This invention relates both to xerography and thermography.

The object of the invention is to combine the advantages of both processes and to eliminate disadvantages of each of them.

Prior thermo processes require thermal-sensitive materials which change color on being heated. Such materials are not normally fixed and hence after the record has been made, the materials are not stable to high temperature. One object of the present invention is to provide a process in which a thermal-sensitive material does not suffer deterioration of the record if exposed to high temperature after the record has been made.

The present invention does not involve a color change in the thermal-sensitive material and hence the choice of materials is not restricted to those which change in color. Furthermore materials suitable for the present invention include such a vast array of different materials that at first glance it would appear that sheet materials made of almost anything would be more or less satisfactory, but this is not quite true and the object of the preferred embodiments of the invention is to provide particularly highly sensitive, highly stable, low cost sensitive sheeting.

Thus it is an object of the invention to provide a reproduction process which is economical and rapid in execution.

The invention takes two general forms. The form in which the final record is made on the sensitive material itself is described in detail below. The form in which the image is transferred to a separate receiving sheet is described in detail in the cofiled application Ser. No. 25,109 entitled Xerothermographic Transfer Process" filed in the names of William J. Dulmage and James G. Jarvis, now abandoned.

Either form is directly applicable to the making of litho masters for lithographic printing. When the record is made on the sensitive material, the image in general is hydrophobic and the sensitive material is hydrophilic or is rendered hydrophilic. In the transfer system, a hydrophobic image is in general transferred to a hydrophilic litho master sheet. Variations of such litho systems are described below.

In the present invention the recording layer is a material which has the property of storing at room temperature an electrostatic charge and of appearing to lose quickly all or part of this charge when heated. There are various theories of how electrostatic charges are stored on the surface of materials and are dissipated, apparently by conductivity, and alternative theories in which the action is analogous to that occurring in electrets giving the appearance of opposite charges on opposite surfaces of the sheet of material; the choice of theory is not critical to the present invention. The present invention is here described in terms of electrostatic charges resting on or at the surface of a material until conducted away or cancelled out by combining with an opposite charge conducted to the surface. It will be understood, however, that the present invention applies whatever theory or model is adopted and the language involving moving charges is here adopted merely for clarity. It is intended to encompass all theories of charge storage and dissipation.

It has been found that many polymeric materials are particularly useful in the present invention. It is apparently possible to use as a recording layer any film forming material which stores an electrostatic charge at room temperature, and which transmits the radiation used in recording. In fact, materials which do not transmit so well could be used in projection printing but the primary use of the invention involves reflex printing and hence requires high transmission. In rare instances some materials show peculiar additional or modified effects but these are not the concern of the present invention and do not eliminate the operation thereof.

Among the large number of useful materials are polyethyleneterephthalate, cellulose acetate, cellulose triacetate, polyethylene, high density polyethylene, polypropylene, vinyl chloride, vinylidene chloride and polystyrene. The recording sheet can be a clear transparent film or a film which has been rendered translucent by pigments or by irregularities such as bubbles, cracks, or scratches on the surface. The polymer can be used as an impregnator or as a coating for support materials such as paper or fabrics. As mentioned above the sheet should transmit highly radiation to be employed in making the reflex printing exposure.

According to the invention an insulating layer such as one of the above-mentioned films whose conductivity (i.e., specific resistance) varies with temperature, is electrostatically charged. Heat is applied, imagewise distributed, to the layer to dissipate the charge. In moving charge theory, it is customary to think of a positive charge on one surface and a negative charge on the opposite surface being dissipated by flowing together through the layer which has been rendered conductive by the high temperature. The remaining charges in the unheated areas are thus distributed imagewise on the surface of the layer. This image is then developed or toned by xerographic methods in which pigment, preferably charged pigment, is applied to the surface of the layer differentially in accordance with the electrostatic charge thereon. In the preferred embodiment of the invention for giving a direct positive, the charged particles are of the same polarity as the charge on the surface so that the particles are attracted to the discharged areas and repelled by the electrostatic image. The charged particles may for example, be in the form of a tribo electric powder or as a suspension'in an insulating liquid.

Tn one embodiment of the invention, the pigment is fuzed or otherwise caused to adhere to the surface.

In a preferred embodiment of the invention the recording sheet is placed in contact with a document and remains there until the reproduction is complete. That is, the recording layer, in contact with the document, is charged, then exposed to radiation, such as infrared, which is absorbed by the image on the document so that the image and the perpendicularly adjacent or corresponding areas of the recording layer are heated. The heat created by absorption in the characters of the document surface, by contact and conduction flows through the recording layer. The flow is radial from each point but the perpendicular flow has the greatest effect on the opposite surface of the recording layer and hence there is very little spreading of the image of each character. In practice, the effect appears confined to the perpendicularly adjacent" areas of the recording layers and the terms corresponding areas and adjacent areas refer to areas so affected. Since the specific resistance of the recording layer decreases as its temperature increases, the heat causes the electrostatic charge to be discharged in corresponding areas of the recording layer. While still in contact with a document, the surface of the recording layer opposite to that which is in contact with the document, is toned by xerographic methods and the toner is fuzed or otherwise (such as by adhesive in the vehicle of a liquid toner) caused to adhere firmly to the surface of the recording layer. The recording layer is then separated from the document.

Since the thermal sensitivity is effective merely to change the electrical conductivity (i.e., specific resistance) of the material and not to change the color in any way, the reproduction is stable to further thennal exposure or heating.

One of the special advantages of the invention in all of its embodiments and particularly in the one in which the sensitive layer is in contact with the document while being charged, is the fact that the electrostatic charge itself causes the recording layer to adhere firmly to the document insuring the extremely good contact which is required for thermal recording by contact. This eliminates the need for pressure on the sandwich, although pressure may still be used if desired for some other reason. In fact electrostatic attraction can be used in straight thermographic processes in place of pressure.

One interesting and sometimes useful feature of the present invention is the fact that it works equally well with charges of either polarity. This is in contrast, for example, to those forms of xerography relying on the photo response of zinc oxide which stores negative charges but allows positive charges to dissipate. A negative or a positive charge may be applied directly to the recording surface by suitable corona discharge device, or in those embodiments of the invention in which the insulating recording layer is used alone (i.e. without any conducting backing) the charge on the recording surface may be induced by corona treatment of the opposite surface. In the preferred embodiment just described, the recording surface is the one opposite to that in contact with the document and this recording surface receives its charge directly from the corona.

While the above processes may be practiced with various types of apparatus, one particularly useful form for such copying involves a rotating drum onto which the sandwich consist- I ing of the document facing up and the recording layer on the outer surface, is fed. This sandwich moves first past an electro static charging station which causes the sandwich to adhere firmly together and to the drums and which also charges the outer surface of the recording layer (and the other surface oppostitely). The rotation of the drum carries the sandwich next under an infrared lamp which by reflex printing through the recording layer heats the image on the document and the adjacent or corresponding areas of the recording layer causing the charge to be dissipated in those areas of the surface. The rotation of the drum then carries the sandwich to a third station at which toner is applied from a powder or liquid developer. If the toner is of a type which does not adhere firmly to the surface at this stage, it is then fuzed before stripping the sandwich from the drum and separating the reproduction from the document. Fuzing may take place after stripping, of course. It is customary to use infrared as the radiation because of the availability of high intensity infrared lamps, but any radiation which is absorbed in adequate quantities by the image on the document is, of course, satisfactory.

A simplified form of this apparatus involves a two-cycle rotation of the drum so that after the image is toned it again passes under the electrostatic charging station which has no adverse effect and tends to improve the adhesion of the toner and then under the exposing station which thus fuzes the toner to the image. The sandwich is then stripped off before it reaches the toner station a second time, or the toner station is moved out of the way during the second half of the cycle in this simplified apparatus.

The cofiled Dulmage and Jarvis application mentioned above has to do with transfer processes employing the present invention and one preferred embodiment thereof has a conducting layer laminated to the insulating recording layer or has the insulating layer coated on a relatively conducting layer such as paper. The coated or impregnated materials have been found to work quite satisfactorily in the direct process (as distinguished from the transfer process) but the laminated materials do not hold the surface charge if the conducting surface faces outward in the direct process. They do work, however, if the conducting layer is in contact with the document since the heat is sharply transmitted through the conducting layer to the insulating layer, but even this orientation of a laminated recording layer has a disadvantage since mechanical means are then required for holding the recording layer to the document, since the electrostatic charge no longer serves to provide the close adhesion produced when an insulating charged layer is in contact with the document.

Lithographic processes employing the present invention, in general, may have practically any of the variations known to lithography (hydrophobic or hydrophilic inks, direct or offset printing, the matrix hydrophilic with hydrophobic characters or vice versa, etc.) However, the invention is particularly useful in two systems, both of which use hydrophobic characters on a hydrophilic background matrix, hydrophobic inks and offset printing.

In the direct form of the invention the hydrophobic toner is fixed to the insulating recording layer whose surface is hydrophilic or is rendered hydrophilic after toning by treatment depending on the material used. In the transfer process, a simple procedure to make a litho master is to transfer the toner image to a standard litho matrix which is subsequently rendered hydrophilic by the usual commercial treatment. Either form of matrix is then used in an offset litho press.

The features and advantages of the invention will be more fully understood from the following examples and particularly from the accompanying drawings in which:

FIG. 1 is a cross section of a simple sheet material suitable for the present invention.

FIG. 2 is a similar cross section, of an alternative form of material.

FIGS. 3A to 3D is a schematic flow chart of a process according to a preferred embodiment of the inventionv FIGS. 4A to 4F similarly show an alternative embodiment of the invention.

FIG. 5, 6 and 7 are schematic cross sections of preferred forms of the apparatus for office copying according to the invention.

FIGS. 8A to 8C illustrate schematically a lithographic process employing a matrix made by the invention.

FIGS. 9A and 9B similarly illustrate an alternative method of making a litho matrix according to the invention.

In FIG. 1 the sheet 10 has high electrical resistance so that when charged by any of the methods commonly used in xerography it retains a negative or positive charge on one surface thereof and the opposite charge on the opposite surface. A particularly useful material is a transparent sheet of polyethylene terephthalate, but other materials transparent of translucent may be used. The essential property of the material is that its electrical conductivity increases when the temperature is raised. With a few rare exceptions this is a property common to all highly insulating materials. Examples of preferred materials are discussed below.

In FIG. 2 the insulating material 11 is laminated to a paper base 12. Alternatively the insulating material can be coated on one or both sides of, or impregnated into, the paper base. A highly preferred material is so-called onion skin paper coated with a vinyl copolymer 0.005 inch on both sides. An example of a preferred copolymer is vinyl chloride/vinyl acetate in a ratio of 87:l3. So called map overlay paper is another thin smooth paper which is quite useful. The paper is preferably thin and smooth to give best resolution but this is not critical since ordinary bond paper gives acceptable resolution and rougher papers give the resolution normally associated with such roughness.

In FIGS. 3A to 3D a recording sheet 10 is placed on top of a document 13 having printed or image areas 14 in contact with the layer I0. Electrostatic charges 15 and charges 16 of opposite polarity to 15 are provided by placing the sandwich on a conducting support 17 and passing the sandwich under a corona discharge wire 18 held at high potential by a source indicated schematically at 19. Either positive or negative corona may be used, the upper surface receiving charges of the same sign as the corona. The charges are represented by circles through the surface, they are considered to be ions at" the surface, i.e. among the molecules forming the surface. The drawing indicates the recording sandwich moving to the right and hence the area which is or has passed under the corona wire 18 is charged and the remaining area is not yet charged in FIG. 3A. The charge has the additional advantage in this embodiment of causing the layer 10 to cling closely to the document 13 with its image characters 14.

In FIG. 3B the electrically charged sandwich is moved under an intense source of radiation 20 such as an infrared lamp with suitable reflector or a high intensity visible lamp which causes radiation to be absorbed by the image 14 which is thus heated and which heats the adjacent area of the recording sheet 10. Thus in area 21 the negative charge is dissipated and the positive charges in contact with the image 14 are similarly dissipated. The material tends to cool down immediately after passing the radiant source, but this has no adverse effect since the image areas have already been discharged during the radiation. It has the advantage, on the other hand, of not dissipating the charge in the non-image areas. Exposure times are selected to give high density (practically complete discharge of the image areas without appreciable spreading of the effect).

The electrostatic image may be developed by any of the standard xerographic methods. In FIG. 3C the sandwich is developed by so-called cascade development in which the toner 25 carrying a negative charge, i.e. the same charge as is on the upper surface of the layer 10, is applied to the surface and allowed to roll across the surface. Particles 26 of toner adhere to the discharged areas of the layer but are repelled by theareas which remain charged after the exposure by the radiant source 20. Thus toner 26 is deposited in the areas corresponding to the image 14.

After the charge has been dissipated in the area 21 as illustrated in FIG. 33 there is a distortion in the electric field between the negative and positive charges, particularly at the edges of the image and at the edges of the film 10 itself. Toner is attracted not only in the center of the discharge areas but particularly at the edges thereof because of this distorted electric field. Thus the edges 27 of the image are particularly sharp and often there is a deposit 28 right at the edge of the film itself. The latter is not objectionable and of course is avoided if the toner is applied only in the center of the recording layer 10. The important point is that the outlining of the edges 27 produces particularly high resolution and particularly clear reproductions. The reproductions are often of even better quality than the original document. This is one of the great advantages of the present process over thermography, xerography and diffusion photographic systems.

In FIGS. 4A to 4D a process similar to that of FIGS. 3A to 7 3D is illustrated, but in this case the more normal, but less preferable procedure is used in which the recording layer is in contact with the document only at the time the exposure is being made. In FIG. 4A the recording 10 is provided with an electrostatic charge by a corona source 18, the back of the layer 10 being in contact with a grounded roller 31. The charged layer 10 is then placed in contact with the document 13 and exposed by an infrared or other high intensity source so that the charges are dissipated in the area 21 as before. There is no real need for a grounded electrode during the exposure stage. However, separating the recording layer 10 from the document 13 before the toning step of FIGS. 4C is likely to cause a distortion of the electric field due to the well known electrostatic effects incurred in separating two materials, one of which is charged. Grounded electrodes or rollers are preferably pressed in contact with the document during separation of the two layers before toning, to minimize the separation static. The results shown in FIG. 4D are similar to those in FIG. 3D however.

FIGS. 4E and 4F are included merely to illustrate the fact that other types of toning can be used. If the toner is applied as a charged spray 32 or as dust particles, uncharged or charged opposite to that of the image on the surface of the recording layer 10 the particles or spray droplets are attracted to the charged areas of the image forming deposit 33 which is a negative compared to the original document 13. This point is mentioned since there are of course some processes in which a negative is desired although simple office copying procedures generally prefer to produce a positive of the document being copied.

All of the above embodiments of the invention and particularly that shown in FIGS. 3A to 3D lend themselves particularly well to drum processing. One suitable printer processor is illustrated in FIG. 5. In this FIG. 5 a large drum 40, preferably grounded, is rotated slowly by an electric motor and gear chain illustrated as a motor 41 and belt 42. At a feeding station corresponding to a shelf 43, a document 13 with image areas 14 is pressed in contact with a recording layer 10 and the sandwich is fed onto the drum 40. The sandwich immediately passes under a charging station consisting of flow discharge wires 45 and the electrostatic charge causes the layers 10 and 13 to adhere to each other, causes the document 13 to adhere to the drum 4 and charges the outer surface of the layer 10 all as discussed in connection with FIG. 3A. Rotation of the drum carries the sandwich to an exposing station at which a lamp 46 illuminates the sandwich, heating the image area 14 and the adjacent areas of the recording layer 10, thus dissipating the charge on the surface of these areas. The sandwich with the electrostatic image thereon then passes a toning station consisting of a rotating brush 50 which applies toner 51 to the surface distributed imagewise in accordance with the electrostatic image. The sandwich then passes under a second infrared source 52 which fuzes the toner to the recording layer forming the image 53 on the surface opposite to that in contact with the original document image 14. The sandwich is stripped from the drum by a stripping member 54.

A somewhat similar but simpler arrangement is shown in FIG. 6. In this case however, after the sandwich has been toned, by the brush 50, the sandwich remains on the drum passing a second time under the glow discharge 45 which may or may not be turned on during this second cycle. The sandwich then passes under the infrared lamp 46 which now acts as the fuzing lamp, fuzing the toner to the recording layer 10. In this case a stripping member 56 which has been held away from the drum during the first cycle is moved as shown by double arrow 57 toward the drum after the sandwich has passed the toning station 50 and before it arrives at the stripping station 56. Thus the sandwich with the fuzed image 53 on the top thereof is stripped from the drum 40 and the reproduction consisting of the layer 10 with the image 53 is separated from the document 13.

The apparatus illustrated in FIG. 7 includes certain refinements but is otherwise similar to that shown in FIG. 5. In FIG. 7 the drum 60 is provided with a thin insulating coating 61 which is electrostatically charged by an auxiliary corona discharge 62 so that the document 13 adheres extra firmly to the drum as the sandwich is passed between the drum 60 and a pressure roller 63 before it reaches the primary charing station 64. The two charging coronas are of opposite polarity. The document 13 is usually conducting and the feeding shelf 43 is preferably grounded so that adherence of the document to the charged layer 61 is insured. In this embodiment the infrared source 65 is located in an elliptical (cylindrical) reflector 66 which concentrates the radiation very intensly as a line across the drum surface. Thus the recording layer is exposed, heated rapidly and allowed to cool immediately thereafter to maintain maximum contrast. In this particular embodiment the toner is applied as a suspension in an insulating liquid 70 which is fed from a reservoir 71 when the valve 72 is opened, through a pipe 73 to impinge on the surface of the drum and specifically on the surface of the recording layer 10 as itpasses the toning station. The overflow from the end of the pipe 73 is pumped by a pump 74 back up to the reservoir 71 to provide the necessary head to cause the flow.

With highly insulating materials such as polyethyleneterephthalate, the latent image can be stored for relatively long periods of time before toning. One such image was stored for 2% days after the thermal exposure had been made and it accepted toning very well.

FIG. 8A is the same as FIG. 30 or FIG. 4D. In FIG. 8A, the material constituting the insulating layer 10 is such that its surface may be hydrolized by treatment with a reagent applied by a brush 80 in FIG. 8B, the hydrolization being indicated by shaded areas 81. There are many chemical reactions which produce this effect. For example cellulose acetate treated with sodium hydroxide becomes hydrophilic. Others are common in lithography.

FIG. 8C represents a litho offset press in which the matrix with hydrophobic image areas 26 and hydrophilic background 81 is wrapped on a drum 85. The matrix is moistened by a roller 86 from a water bath or fountain solution 87, then inked by a roller 88 which applies to the image areas 26, a greasy ink 89 which is repelled by wetted areas 81. The ink transfers to a FIGS. 9A and 9B are representative of those materials and systems in which hydrophilicity is caused by radiation. In FIG. 9B corona discharge (with its electron, ultra violet and visible radiation) is produced between a high potential wire 95 and a grounded roller 96. Polyethylene has a surface which is rendered hydrophilic by such a treatment. Since many hydrophilic materials do not hold a charge so as to be useful in the present invention, it is interesting to note that only the surface need be hydrophilic and the layer may still be highly insulating. For example, polyethylene sheeting pretreated with corona has a hydrophilic surface but can be used quite successfully as the recording layer. Thus the toner is applied to a material which is already hydrophilic and is immediately ready as a litho matrix. Since the surface is rendered hydrophilic before the charging step, this can be done during manufacture of the material and thus is preferable.

EXAMPLE 1 A printed document was covered with 0.002 inch thick sheet of cellulose acetate. The top surface of the acetate was subjected to a negative corona while the rear surface of the document was in contact with a grounded conductor. The sandwich was exposed in a standard therrnographic copier to an infrared source. The resulting electrostatic image was cascade developed using standard xerographic toning powders. The image was covered with a thin non-adhering protective sheet of polyethylene and passed under an infrared lamp, specifically by passing it a second time through the standard copier. The resulting image was sharp, of a high density and firmly attached to the acetate sheet. The reproduction is especially permanent since both the image and the sheet are especially stable materials.

EXAMPLE 2 Repeated Example 1 using 0.00! inch thick sheet of transparent polyethylene terephthalate.

EXAMPLE 3 An image was prepared as in Example 1 using 0.002 inch thick sheet of cellulose acetate and after toning and fuzing, as in Example 1 the surface of the sheet was hydrolyzed with a sodium hydroxide solution which rendered the untoned areas of the cellulose acetate hydrophilic while the toner remained hydrophobic. Several hundred litho prints were made using this sheet material in a standard litho offset press.

EXAMPLE 4 An image was prepared according to Example 3 using a 0.002 inch thick sheet of polyethylene. The (non-image) untoned areas of the polyethylene were rendered hydrophilic by exposure to an intense corona discharge. The toner remains hydrophobic under this treatment and the sheet was used as a litho master in a standard litho offset press and again several hundred prints were made.

EXAMPLE 5 A latent image was prepared according to Example 1 using a 0.0015 inch sheet of polyethylene terephthalate. Toning was provided by developing the electrostatic image in a cyclohexanol bath containing negatively charged particles and a small amount of styrene-alkyd resin to serve as a binder. Thus the fuzing step was eliminated. EXAMPLE 6 An image was prepared according to Example 1 using a relatively thick (0.008 inch) cellulose acetate sheet pigmented with titanium. dioxide. This sheet is non-transparent and quite white," but even though it was of great thickness it was found possible to record a useful, quite legible image of a document with 6-point type.

EXAMPLE 7 Polyethylene and polypropylene coated impregnated papers capable of storing a charge (those which were not insulators and thus not capable of storing a charge were not useful) were found to give good image quality when used as in Example I providing there were no excessive inhomogeneities or irregularities in the paper or in the coating.

A large number of specific polymers, resins and esters are described in the cofiled Dulmage and Jarvis application mentioned above. They are thus useful in the present invention. They are also useful in the specific embodiments discussed above in which the image or litho master is formed directly on the recording layer.

Having thus described various embodiments of the invention it will be understood that the invention is not limited to those embodiments but is of the scope of the appended claims.

I claim:

1. The reproduction process comprising electrostatically charging an insulating layer whose conductivity varies with temperature, applying heat to the layer imagewise distributed to selectively dissipate the charge through the layer and thus to distribute the electrostatic charge imagewise on the surface of the layer and applying pigment to the surface of the layer differentially in accordance with the electrostatic charge thereon.

2. The process according to claim 1 including the added step of fuzing the pigment to the surface.

3. The process according to claim 1 in which the layer transmits an exposing radiation and in which the heat applying step consists of placing the layer in contact with the surface of a document to be reproduced, which contact is firm at least partly due to the electrostatic charge, and exposing the document through the layer to radiation absorbed by the image on the document.

4. The process according to claim 1 in which the pigment is attracted to the discharged areas of the layer.

5. The process according to claim 1 in which the pigment is hydrophobic and including the steps of rendering the surface of the layer hydrophilic and after said rendering and said applying of pigment, litho printing by offset from the imagewise pigmented surface of the layer.

6. The process according to claim 5 in which the surface of the layer is rendered hydrophilic before said charging.

7. The reproduction process comprising placing in contact with the surface of a document to be reproduced an insulating, radiation transmitting, layer whose conductivity varies with temperature, electrostatically charging the surface of the layer opposite to the document, exposing the surface of the document to radiation through the layer to differentially heat the document in accordance with the image thereon and correspondingly to heat the adjacent areas of the insulating layer to allow the electrostatic charge to leak through the layer in the heated areas, applying pigment to the surface of the layer opposite to the document differentially in accordance with the charge thereon and removing the layer from the document.

8. The process according to claim 7 in which the pigment is charged the same as the electrostatic charge on the surface to be repelled thereby and to be attracted to the discharged areas of the surface.

9. The process according to claim 7 in which the pigment is hydrophobic and including the steps of rendering the surface of the layer hydrophilic and after said rendering and said ap-- plying of pigment, litho printing by offset from the imagewise pigmented surface of the layer.

10. The process according to claim 9 in which the surface of the layer is rendered hydrophilic before said charging.

11. A photographic reproduction process which comprises directly exposing an electrostatically charged electrothermographic layer to heat rays while positioned adjacent to the master, the heat rays being transmitted through the layer to the master, and developing the resulting image with an electroscopic material.

12. A process according to claim 11 in which the layer is on one side only of a support.

13. A process according to claim 11 in which the layer is on both sides of a support.

14. A process according to claim 11 in which the layer is self-supporting.

15. A process according to claim 11 in which the layer is charged prior to being positioned adjacent the master.

16. A process according to claim 11 in which the layer is charged after being positioned adjacent the master.

17. A process according to claim 11 in which the layer is supported and exposed to heat with the layer facing away from the master.

18. A process for producing electrostatic images which comprises subjecting a supported layer consisting essentially of a resin, having a specific resistance which decreases with increasing temperature, to an electrostatic charge and exposing the charged layer to radiant heat under a pattern for a time and at a temperature sufficient to produce a latent electrostatic image on the layer.

19. A process according to claim 18 in which the support is paper.

20. A process for producing electrostatic images which comprises coating a support with a layer consisting essentially of a resin, having a specific resistance which decreases with increasing temperature, subjecting the supported layer to an electrostatic charge and exposing the charged layer to radiant heat under a pattern for a time and at a temperature sufiicient to produce a latent electrostatic image on the layer.

21. A process according to claim 20 in which the support is paper.

22. A process according to claim 20 in which the image is developed by treatment with powder. 

2. The process according to claim 1 including the added step of fuzing the pigment to the surface.
 3. The process accorDing to claim 1 in which the layer transmits an exposing radiation and in which the heat applying step consists of placing the layer in contact with the surface of a document to be reproduced, which contact is firm at least partly due to the electrostatic charge, and exposing the document through the layer to radiation absorbed by the image on the document.
 4. The process according to claim 1 in which the pigment is attracted to the discharged areas of the layer.
 5. The process according to claim 1 in which the pigment is hydrophobic and including the steps of rendering the surface of the layer hydrophilic and after said rendering and said applying of pigment, litho printing by offset from the imagewise pigmented surface of the layer.
 6. The process according to claim 5 in which the surface of the layer is rendered hydrophilic before said charging.
 7. The reproduction process comprising placing in contact with the surface of a document to be reproduced an insulating, radiation transmitting, layer whose conductivity varies with temperature, electrostatically charging the surface of the layer opposite to the document, exposing the surface of the document to radiation through the layer to differentially heat the document in accordance with the image thereon and correspondingly to heat the adjacent areas of the insulating layer to allow the electrostatic charge to leak through the layer in the heated areas, applying pigment to the surface of the layer opposite to the document differentially in accordance with the charge thereon and removing the layer from the document.
 8. The process according to claim 7 in which the pigment is charged the same as the electrostatic charge on the surface to be repelled thereby and to be attracted to the discharged areas of the surface.
 9. The process according to claim 7 in which the pigment is hydrophobic and including the steps of rendering the surface of the layer hydrophilic and after said rendering and said applying of pigment, litho printing by offset from the imagewise pigmented surface of the layer.
 10. The process according to claim 9 in which the surface of the layer is rendered hydrophilic before said charging.
 11. A photographic reproduction process which comprises directly exposing an electrostatically charged electrothermographic layer to heat rays while positioned adjacent to the master, the heat rays being transmitted through the layer to the master, and developing the resulting image with an electroscopic material.
 12. A process according to claim 11 in which the layer is on one side only of a support.
 13. A process according to claim 11 in which the layer is on both sides of a support.
 14. A process according to claim 11 in which the layer is self-supporting.
 15. A process according to claim 11 in which the layer is charged prior to being positioned adjacent the master.
 16. A process according to claim 11 in which the layer is charged after being positioned adjacent the master.
 17. A process according to claim 11 in which the layer is supported and exposed to heat with the layer facing away from the master.
 18. A process for producing electrostatic images which comprises subjecting a supported layer consisting essentially of a resin, having a specific resistance which decreases with increasing temperature, to an electrostatic charge and exposing the charged layer to radiant heat under a pattern for a time and at a temperature sufficient to produce a latent electrostatic image on the layer.
 19. A process according to claim 18 in which the support is paper.
 20. A process for producing electrostatic images which comprises coating a support with a layer consisting essentially of a resin, having a specific resistance which decreases with increasing temperature, subjecting the supported layer to an electrostatic charge and exposing the charged layer to radiant heat under a pattern for a time and at a temperature sufficient to produce a latent electrostatic image on the Layer.
 21. A process according to claim 20 in which the support is paper.
 22. A process according to claim 20 in which the image is developed by treatment with powder. 